This invention relates to fuzes for submunitions, and, more particularly, to a fuze structure that improves the reliability of operation, safety and effectiveness of military grenades and other explosive devices.
Submunitions are weapons of war. Examples include anti-personnel land mines, shoulder fired missiles, warheads, bomblets, anti-armor devices, blast fragmenting devices and grenades, some of which are carried by a carrier and are expelled as the carrier approaches the target. Of the foregoing submunitions, the grenade, which is used by artillery projectiles (shells), multiple-launch rocket systems, and extended range mortars, is the smallest in size. That small size imposes a significant physical constraint on the size of an installed fuze, and, indirectly, on the effectiveness and reliability of the fuze.
Consider the operation of the present grenade fuze, which, typically, detonates the grenade on impact through use of a stab detonator. Propelled from a grenade carrier, the grenade spins at a high RPM while traveling forward at a high velocity. A nylon ribbon is extended from the grenade, which orients the grenade with respect to the ground. An end of that ribbon is attached to a threaded firing pin inside the grenade. As the grenade falls, the drag of the ribbon to the rotation of the grenade produces a relative rotational force between the grenade and ribbon.
That rotational force turns the threaded firing pin out of a threaded socket in a slider, disengaging the tip of the firing pin from the slider and unthreading the firing pin into an inertial weight. Released from the hold of the pin, the slider is forced radially outward by the combination of the centrifugal force of the rotating grenade and an arming spring to a radial position at which the stab detonator (e.g. firing pin) carried in the grenade becomes aligned with the lead explosive charge. At that point in the flight, the grenade becomes fully armed, and the arming spring holds the slide in that fully armed position. On impact with the target or other mass, the stab detonator initiates the explosive train through contact with the lead charge at a high velocity. As stored for use, the tip end of the threaded firing pin engages the slider and prevents the slider from moving into position. Since the slider must be moved in order for the explosive to detonate, the grenade cannot be detonated, and, as stored, is safe.
An electromechanical self-destruct (xe2x80x9cSDxe2x80x9d) mode is typically included in the existing grenade fuze as a back up. That includes a battery ampule, an electronic timer, and a capacitor. When the slider is forced radially outward, a spiral locking mechanism releases a battery activator, which ruptures an ampule of a reserve battery. During the movement of that activator, an electrical short-circuit is also removed so that the battery charges activates the electronic timer. After the lapse of a predetermined time, the capacitor discharges into the electro-explosive device next to the detonator, which causes the munition to function.
The foregoing prior art fuze occupies a significant portion of the package of the grenade and relies solely upon a series of mechanical operations to arm and ready the grenade for detonation. Should any of those mechanical operations fail to fully function as designed, the result is an unexploded grenade, a xe2x80x9cdudxe2x80x9d.
The portion of the grenade volume not occupied by the fuze is filled with explosive. The greater the volume of explosive in the grenade, the greater the force that is produced on detonation. By reducing the volume of the fuze for a grenade of a given size, a more powerful grenade may be realized. However, the foregoing stab detonator type of fuze represents the smallest size for the fuze elements that has been demonstrated to date, and, presumably is the smallest size grenade fuze known to the art.
Accordingly, a principal object of the invention is to significantly reduce the physical volume (e.g. size) of the fuze used in submunitions.
A further object of the invention is to enhance the explosive power of existing submunitions.
An additional object of the invention is to miniaturize grenade fuzes.
A still further object of the invention is increasing the safety of submunitions for those who use the submunition.
Unintended operation and safety of an explosive is also of concern in fields outside of submunitions. Two devices used in those fields to ensure safety and avoid inadvertent operation are known, respectively, as a xe2x80x9carm-firexe2x80x9d device and a xe2x80x9csafe and armxe2x80x9d device. In order to prevent a rocket motor, warhead, explosive separation device or energetic material, collectively sometimes referred to as target devices, from being unintentionally operated during flight or in any circumstance that could produce an extreme hazard to personnel or facilities, an arm-fire device is customarily incorporated in the firing control circuit of the foregoing devices. The arm-fire device electrically and mechanically interrupts the ignition train to the target device to prevent accidental operation.
The arm-fire device includes a mechanism that permits the target device to be armed, ready to fire, only while electrical power is being applied to the target device. When that electrical power is removed, the mechanism of the arm-fire device returns to a safe position, interrupting the path of the ignition train, signifying the target device is disarmed. Arm-fire devices typically use xe2x80x9cthrough-bulkheadxe2x80x9d initiators to transfer energy through a bulkhead from the arm-fire device on one side of the bulkhead to an acceptor device on the other side.
The safe and arm device is a variation of the arm-fire device. The mechanism of the safe and arm device enables a target device to remain armed, even after electrical power is removed. The device may be returned to a safe position only by again applying (or reapplying) electrical power. The safe and arm device is commonly used to initiate a system destruct in case of a test failure, for launch vehicle separation and for rocket motor stage separation during flight. Typically, the safe and arm device uses a pyrotechnic output (e.g. explosive train) which may be either a subsonic pressure wave or which may be a flame front and supersonic shock wave or detonation to transfer energy to another pyrotechnic device (and serves as the trigger of the latter device).
Although the latter two devices possess functions similar to that of the grenade fuze, the latter is entirely mechanical in operation. In contrast, the arm-fire device requires an electrical source to start and maintain operation and the safe and arm device must be armed by application of an electrical source and requires reapplication of an electrical source to disarm. Importantly, the latter devices have been the size of a person""s fist and possess a noticeable weight of several pounds, rendering them impractical for application in the fuze of a submunition, and, particularly impractical for application in grenades. As an advantage, the present invention is able to apply those kinds of devices within a grenade fuze.
A recent innovation co-invented by a co-inventor of the present invention defines new structure for arm-fire devices and safe and arm devices in which the size and weight of the foregoing devices is dramatically reduced. Those small size devices benefit from the application of micro-electromechanical systems (xe2x80x9cMEMSxe2x80x9d) technology. Reference is made to the copending U.S. patent application, Ser. No. 09/665,230, filed Sep. 18, 2000, entitled MEMS Arm Fire and Safe and Arm Devices, now U.S. Pat. No. 6,431,071 B1 assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference. The foregoing application describes a new design for both arm-fire devices and safe and arm devices in a microminature size. As an advantage, the fuze of the present invention incorporates the foregoing devices as a component.
Accordingly, a further object of the invention is to adapt MEMS arm-fire devices and safe and arm devices as a component of a fuze.
And a still further object of the invention is to provide an electrically operated fuze for submunitions, including grenades.
After a battle has been won, a remaining concern is clearing the battlefield of any unexploded submunitions, duds, so that one""s troops and civilians may walk over the land without fear. The desire is to make the battlefield safe. Doing so is a difficult task, principally because of the difficulty of locating the dud. Even today, live shells from World War I continue to be uncovered from the battlefields of France, and some areas of land remain off-limits to this day. As an advantage, the present invention provides a fuze that may be destroyed by remote control.
A further object, thus, is to provide a more efficient and easy way to clear a battlefield of unexploded submunitions.
In accordance with the foregoing objects and advantages, the fuze invention includes a MEMS velocity sensor, a MEMS shock detector, a DC power supply and one of the MEMS arm-fire device or MEMS safe and arm device.
The velocity sensor, suitably a MEMS three-axis accelerometer, provides a signal when the grenade is at or above a predetermined velocity, which occurs only after the grenade is propelled from the grenade carrier safely distant from operational personnel. Responsive to that signal, the respective arm-fire device or safe and arm device is placed in an armed state. The MEMS shock detector, also suitably a MEMS three-axis accelerometer, supplies a signal when the grenade impacts a target. Responsive to that signal the respective arm-fire device or safe and arm device is fired, which initiates detonation of the high explosive charge carried in the grenade.
An additional feature of the invention comprises combining a pair of identical individual fuzes in a single package to provide a more reliable fuze for each submunition. Each fuze occupies a volume that is a small fraction of the volume of the prior grenade fuzes. The pair of those fuzes is also significantly less in volume and weight than the prior grenade fuzes. As an advantage, the foregoing fuze redundancy provides a fuze of greater reliability than the prior stab detonators of the prior art, reducing the likelihood of a dud. Should one of the two fuzes (or sub-fuzes) in the package fail, it is highly unlikely that the second in the pair would also fail.
As a still further feature to the invention, the fuze may include a RF receiver decoder. The output of the receiver decoder is coupled to the explosive initiator in fuze, whereby the broadcast of a coded broadcast signal results in detonation of the submunition. As an advantage, the invention eliminates the need to search for duds and the destruction of those submunitions is no more complicated than closing a switch.
The foregoing and additional objects and advantages of the invention, together with the structure characteristic thereof, which were only briefly summarized in the foregoing passages, will become more apparent to those skilled in the art upon reading the detailed description of a preferred embodiment of the invention, which follows in this specification, taken together with the illustrations thereof presented in the accompanying drawings.